Selective catalytic reduction articles and systems

ABSTRACT

Certain selective catalytic reduction (SCR) articles, systems and methods provide for high NOx conversion while at the same time low N 2 O formation. The articles, systems and methods are suitable for instance for the treatment of exhaust gas of diesel engines. Certain articles have zoned coatings containing copper-containing molecular sieves disposed thereon, where for example a concentration of catalytic copper in an upstream zone is lower than the concentration of catalytic copper in a downstream zone.

The present invention is aimed at selective catalytic reduction (SCR)articles and systems suitable for use in treating exhaust of an internalcombustion engine.

BACKGROUND

Molecular sieves such as zeolites are employed in the catalysis ofcertain chemical reactions for example the selective catalytic reduction(SCR) of nitrogen oxides with a reductant such as ammonia, urea orhydrocarbons. Zeolites are crystalline materials having rather uniformpore sizes which, depending upon the type of zeolite and the type andamount of cations included in the zeolite lattice, range from about 3 toabout 25 angstroms in diameter. Zeolites having 8-ring pore openings anddouble-six ring secondary building units, particularly those havingcage-like structures are of interest as SCR catalysts. Included in thiscategory are zeolites having a chabazite (CHA) crystal structure, whichare small pore zeolites with 8 member-ring pore openings (ca. 3.8angstroms) accessible through its 3-dimensional porosity. A cage likestructure results from the connection of double six-ring building unitsby 4 rings.

Catalysts employed in the SCR process ideally should be able to retaingood catalytic activity over the wide range of temperature conditions ofuse, for example from about 150° C. to about 600° C. or higher, underhydrothermal condition s. Hydrothermal conditions are encountered inpractice because water is a byproduct of fuel combustion and hightemperature hydrothermal conditions occur in diesel exhaustapplications, such as during the regeneration of a soot filter, acomponent of exhaust gas treatment systems used for the removal ofcarbonaceous particles.

The SCR process converts nitrogen oxides (NOx) to nitrogen (N₂) andwater (H₂O). An undesired SCR byproduct is nitrous oxide (N₂O). Desiredare improved articles, systems and processes to selectively convert NOxwithin internal combustion engine exhaust streams to N₂ while minimizingthe formation of undesired N₂O. Undesired N₂O formation may be observedas molar percent conversion of (NO+NO₂) to N₂O.

Nitrogen oxides (NOx) may include N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅ or NO₃.

SUMMARY

In one or more embodiments, the present disclosure provides catalyticarticles, systems and methods for treating exhaust gas streamscontaining nitrogen oxides. The articles, systems and methods willexhibit high NOx conversion while at the same time minimize N₂Oformation. In certain embodiments, the articles, systems and methods aresuitable for treating lean exhaust gas streams of diesel internalcombustion engines.

In one or more embodiments, the present disclosure relates to selectivecatalytic reduction articles, systems incorporating such articles, andmethods utilizing such articles and systems. The selective catalyticreduction articles advantageously provide for high NOx conversion withsimultaneously low formation of N₂O because of the utilization of atleast two different catalytically active molecular sieves. Morespecifically, at least a first copper-containing molecular sieve and asecond copper-containing molecular sieve are utilized. Thecopper-containing molecular sieves are coated on at least one substrate.For example, a first coating layer of the first copper-containingmolecular sieve and a second coating layer of the secondcopper-containing molecular sieve are coated on the at least onesubstrate. The first and second coating layers can be coated on the samesubstrate or on different substrates. For example, a first substrate canhave the first coating layer with the first copper-containing molecularsieve provided thereon (e.g., in the form of a washcoat), and a secondsubstrate can have the second coating layer with the secondcopper-containing molecular sieve provided thereon (e.g., in the form ofa washcoat). Preferably, the first substrate with the first coatinglayer is provided upstream of the second substrate with the secondcoating layer relative to the flow path of an exhaust stream (the secondsubstrate with the second coating layer thus being downstream of thefirst substrate with the first coating layer). Also preferably, thefirst copper-containing molecular sieve in the first coating layer insuch configuration will have a copper concentration that is lower than acopper concentration of the second copper-containing molecular sieve inthe second coating layer. The coating layers thus differ because of thediffering copper concentrations. As another example, a substrate canhave a first coating layer with a first copper-containing molecularsieve provided thereon (e.g., in the form of a washcoat), and the samesubstrate can have a second coating layer with the secondcopper-containing molecular sieve provided thereon (e.g., in the form ofa washcoat). In such configuration, the second coating layer ispreferably provided downstream of the first coating layer relative tothe flow path of an exhaust stream (the first coating layer thus beingupstream from the second coating layer). Also preferably, the firstcopper-containing molecular sieve in the first coating layer in suchconfiguration will have a copper concentration that is lower than acopper concentration of the second copper-containing molecular sieve inthe second coating layer. The substrate is thus zoned so that a firstzone includes the first coating layer and the second zone includes thesecond coating layer. The zones (and thus the coating layers) mayoverlap if desired or may be non-overlapping. It has been found thatproviding a first copper-containing molecular sieve with a first copperconcentration and a second copper-containing molecular sieve with asecond, higher copper concentration beneficially achieves the resultsdescribed herein in relation to NOx conversion and low N₂O formation,particularly when the first copper-containing molecular sieve with thelower copper concentration is positioned upstream from the secondcopper-containing molecular sieve with the higher copper concentration.The present disclosure particularly provides, in some embodiments, aselective catalytic reduction article comprising a substrate having afront upstream end and a rear downstream end defining an axial lengthand having a catalytic coating thereon, where the catalytic coatingcomprises a first coating layer comprising a first copper-containingmolecular sieve and a second coating layer comprising a secondcopper-containing molecular sieve.

Advantageously, the article is zoned and comprises a first upstream zonecomprising the first coating layer comprising the firstcopper-containing molecular sieve and a second downstream zonecomprising the second coating layer comprising the secondcopper-containing molecular sieve.

The concentration of copper in the upstream zone may be less than orequal to the concentration of copper in the downstream zone and/or thefirst molecular sieve may contain less copper than the second molecularsieve and/or the concentration of the copper-containing molecular sievein the upstream zone may be less than or equal to the concentration ofthe copper-containing molecular sieve in the downstream zone.

Also disclosed are selective catalytic reduction systems comprising afirst selective catalytic reduction article comprising a first substratecomprising the first catalytic coating layer comprising the firstcopper-containing molecular sieve and a second selective catalyticreduction article comprising a second substrate comprising the secondcatalytic coating layer comprising the second copper-containingmolecular sieve, where the first and second articles are in fluidcommunication and where for example the second article is downstream ofthe first article.

Also disclosed are selective catalytic reduction articles or systemscapable of providing NOx conversion of ≥90% (preferably ≥99%) and N₂Oformation of ≤50% (preferably ≤40%) of that of an article or system,respectively, containing a uniform concentration of CuCHA as the onlySCR catalyst under transient engine testing conditions. Moreparticularly, selective catalytic reduction articles, systems, ormethods of the present disclosure can be configured for providing >90%NOx conversion while also providing 40% N₂O formation, particularly whencompared to an article, system, or method containing or employing auniform concentration of high Cu-containing CuCHA as the only SCRcatalyst under transient engine testing conditions as otherwisedescribed herein. Embodiments of the present disclosure also relate toimproved performance by utilizing zoning. For example, a selectivecatalytic reduction article, system, or method according to the presentdisclosure can include a substrate with a front upstream zone includinga catalytic coating and a second downstream zone including a catalyticcoating, and can be adapted for providing >90% total NOx conversion,particularly wherein the front upstream zone provides from about 30% toabout 80% of the total NOx conversion.

Also disclosed are exhaust gas treatment systems comprising thepreceding SCR articles or SCR systems.

Also disclosed are methods for treating exhaust streams containing NOx,the methods comprising passing the exhaust stream through the precedingSCR article, SCR system or exhaust gas treatment system.

The present articles, systems and methods are in particular suitable forthe treatment of exhaust generated from diesel engines, which operate atcombustion conditions with air in excess of that required forstoichiometric combustion, i.e., lean.

The invention includes, without limitation, the following embodiments.

Embodiment 1: A selective catalytic reduction article comprising asubstrate having a front upstream end and a rear downstream end definingan axial length of the substrate and having a catalytic coating thereon,wherein the catalytic coating comprises: a first coating layercomprising a first copper-containing molecular sieve; and a second,different coating layer comprising a second copper-containing molecularsieve.

Embodiment 2: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the catalytic coating is zoned andcomprises: a first zone proximate to the front upstream end of thesubstrate, the first zone including the first coating layer comprisingthe first copper-containing molecular sieve; and a second zone proximateto the rear downstream end of the substrate, the second zone includingthe second coating layer comprising the second, differentcopper-containing molecular sieve.

Embodiment 3: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the first copper-containing molecularsieve in the first zone has a copper concentration that is less than orequal a copper concentration of the second, different copper-containingmolecular sieve in the second zone.

Embodiment 4: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the substrate is a porous wall-flowfilter or a flow-through monolith.

Embodiment 5: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the first copper-containing molecularsieve comprises copper oxide in an amount of about 0.1 to about 4 wt %,and the second copper-containing molecular sieve comprises copper oxidein an amount of about 3 to about 10 wt %, based on the total weight ofthe molecular sieve.

Embodiment 6: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the first copper-containing molecularsieve comprises copper oxide in an amount of about 1 to about 2.5 wt %,and the second copper-containing molecular sieve comprises copper oxidein an amount of about 3 to about 6 wt %, based on the total weight ofthe molecular sieve.

Embodiment 7: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein a Cu/Al atomic ratio for each of thefirst copper-containing molecular sieve and the second copper-containingmolecular sieve is independently about 0.05 to about 0.55, and whereinthe Cu/Al atomic ratio of the first copper-containing molecular sieve isless than the Cu/Al atomic ratio of the second copper-containingmolecular sieve.

Embodiment 8: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the first coating layer extends adistance from the front, upstream end of the substrate towards the rear,downstream end of the substrate and overlays a portion of the secondcoating layer, which extends from the rear, downstream end of thesubstrate a distance towards the front, upstream end of the substrate.

Embodiment 9: The selective catalytic reduction article of any precedingor subsequent embodiment, wherein the first coating layer extends a fromthe front, upstream end of the substrate to the rear, downstream end ofthe substrate and overlays an entirety of the second coating layer,which extends from the rear, downstream end of the substrate to thefront, upstream end of the substrate.

Embodiment 10: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the second coating layerextends a distance from the front, upstream end of the substrate towardsthe rear, downstream end of the substrate and overlays a portion of thefirst coating layer, which extends a distance from the rear, downstreamend of the substrate towards the front, upstream end of the substrate.

Embodiment 11: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the second coating layerextends from the front, upstream end of the substrate to the rear,downstream end of the substrate and overlays an entirety of the firstcoating layer, which extends from the rear, downstream end of thesubstrate to the front, upstream end of the substrate.

Embodiment 12: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the first coating layer andthe second coating layer are adjacent and do not overlay each other.

Embodiment 13: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the first coating layer andthe second coating layer are in direct contact with each other.

Embodiment 14: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the first copper-containingmolecular sieve and the second copper-containing molecular sieves areeach 8-ring small pore molecular sieves.

Embodiment 15: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the first copper-containingmolecular sieve and the second copper-containing molecular sieve areboth independently zeolites having a structure selected from the groupconsisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT and SAV.

Embodiment 16: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein each of the firstcopper-containing molecular sieve and the second copper-containingmolecular sieve have a CHA crystal structure.

Embodiment 17: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein each of the firstcopper-containing molecular sieve and the second copper-containingmolecular sieve are aluminosilicate zeolites having a CHA crystalstructure and a silica to alumina ratio (SAR) of about 5 to about 40.

Embodiment 18: The selective catalytic reduction article of anypreceding or subsequent embodiment, wherein the substrate includes anundercoat comprising an AMOx catalyst in the second zone.

Embodiment 19: A selective catalytic reduction system comprising: afirst selective catalytic reduction article comprising a first substrateincluding a first catalytic coating layer comprising a firstcopper-containing molecular sieve having a first amount of copper oxide;and a second selective catalytic reduction article comprising a secondsubstrate including a second catalytic coating layer comprising a secondcopper-containing molecular sieve having a second amount of copper oxidethat is greater than the first amount of copper oxide; wherein the firstselective catalytic reduction article and the second selective catalyticreduction article are in fluid communication.

Embodiment 20: The selective catalytic reduction system of any precedingor subsequent embodiment, wherein the first substrate of the firstselective catalytic reduction article is zoned so as to include a firstcatalytic coating layer with a first copper concentration and a secondcocatalyst layer with a second copper concentration that is higher thanthe first copper concentration.

Embodiment 21: The selective catalytic reduction system of any precedingor subsequent embodiment, wherein the first substrate and the secondsubstrate are each independently selected from the group consisting of aporous wall-flow filter and a flow-through monolith.

Embodiment 22: The selective catalytic reduction system of any precedingor subsequent embodiment, wherein the second substrate includes anundercoat comprising an AMOx catalyst.

Embodiment 23: An exhaust gas treatment system comprising: a selectivecatalytic reduction article or a selective catalytic reduction systemaccording to any preceding or subsequent embodiment; and a reductantinjector in fluid communication with and upstream of the selectivecatalytic reduction article or the selective catalytic reduction system.

Embodiment 24: The exhaust gas treatment system of any preceding orsubsequent embodiment, further comprising one or more of a dieseloxidation catalyst, a soot filter, and an ammonia oxidation catalyst.

Embodiment 25: The exhaust gas treatment system of any preceding orsubsequent embodiment, further comprising an internal combustion enginein fluid communication with and upstream of the selective catalyticreduction article or the selective catalytic reduction system.

Embodiment 26: A method for treating an exhaust stream containing NOx,comprising passing the exhaust stream through a selective catalyticreduction article, a selective catalytic reduction system, or an exhaustgas treatment system of any preceding or subsequent embodiment.

These and other features, aspects, and advantages of the disclosure willbe apparent from a reading of the following detailed descriptiontogether with the accompanying drawings, which are briefly describedbelow. The invention includes any combination of two, three, four, ormore of the above-noted embodiments as well as combinations of any two,three, four, or more features or elements set forth in this disclosure,regardless of whether such features or elements are expressly combinedin a specific embodiment description herein. This disclosure is intendedto be read holistically such that any separable features or elements ofthe disclosed invention, in any of its various aspects and embodiments,should be viewed as intended to be combinable unless the context clearlydictates otherwise. Other aspects and advantages of the presentinvention will become apparent from the following.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to provide an understanding of embodiments of the invention,reference is made to the appended drawings, which are not necessarilydrawn to scale, and in which reference numerals refer to components ofexemplary embodiments of the invention. The drawings are exemplary only,and should not be construed as limiting the invention.

FIG. 1 is a perspective view of a honeycomb-type substrate carrier whichmay comprise a catalyst article in the form of a washcoat composition inaccordance with the present invention;

FIG. 2 is a partial cross-sectional view enlarged relative to FIG. 1 andtaken along a plane parallel to the end faces of the substrate carrierof FIG. 1, which shows an enlarged view of a plurality of the gas flowpassages shown in FIG. 1, in an embodiment wherein the substrate carrieris a monolithic flow-through substrate;

FIG. 3 is a cutaway view of a section enlarged relative to FIG. 1,wherein the honeycomb-type substrate carrier in FIG.1 represents a wallflow filter substrate monolith; and

FIG. 4a -FIG. 4j are partial cross-sections showing coating layersand/or coating zones on one or more substrates according to exemplaryembodiments of the present disclosure.

DETAILED DISCLOSURE

Molecular sieves refer to materials having an extensivethree-dimensional network of oxygen ions containing generallytetrahedral type sites and having a pore distribution of relativelyuniform pore size. A zeolite is a specific example of a molecular sieve,further including silicon and aluminum. Reference to a“non-zeolite-support” or “non-zeolitic support” in a catalyst layerrefers to a material that is not a zeolite and that receives preciousmetals, stabilizers, promoters, binders and the like throughassociation, dispersion, impregnation or other suitable methods.Examples of such non-zeolitic supports include, but are not limited to,high surface area refractory metal oxides. High surface area refractorymetal oxide supports can comprise an activated compound selected fromthe group consisting of alumina, zirconia, silica, titania, ceria,lanthana, baria and combinations thereof.

Present molecular sieves for instance have 8-ring pore openings anddouble-six ring secondary building units, for example, those having thefollowing structure types: AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS,SAT or SAV. Included are any and all isotopic framework materials suchas SAPO, AIPO and MeAPO materials having the same structure type.

Aluminosilicate zeolite structures do not include phosphorus or othermetals isomorphically substituted in the framework. That is,“aluminosilicate zeolite” excludes aluminophosphate materials such asSAPO, AlPO and MeAPO materials, while the broader term “zeolite”includes aluminosilicates and aluminophosphates.

The 8-ring small pore molecular sieves include aluminosilicates,borosilicates, gallosilicates, MeAPSOs and MeAPOs. These include, butare not limited to SSZ-13, SSZ-62, natural chabazite, zeolite K-G, LindeD, Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47,ZYT-6, CuSAPO-34, CuSAPO-44 and CuSAPO-47. In specific embodiments, the8-ring small pore molecular sieve will have an aluminosilicatecomposition, such as SSZ-13 and SSZ-62.

In one or more embodiments, the 8-ring small pore molecular sieve hasthe CHA crystal structure and is selected from the group is consistingof aluminosilicate zeolite having the CHA crystal structure, SAPO, AlPO,and MeAPO. In particular, the 8-ring small pore molecular sieve havingthe CHA crystal structure is an aluminosilicate zeolite having the CHAcrystal structure. In a specific embodiment, the 8-ring small poremolecular sieve having the CHA crystal structure will have analuminosilicate composition, such as SSZ-13 and SSZ-62.Copper-containing chabazite is abbreviated as CuCHA.

Molecular sieves can be zeolitic (zeolites) or may be non-zeolitic. Bothzeolitic and non-zeolitic molecular sieves can have the chabazitecrystal structure, which is also referred to as the CHA structure by theInternational Zeolite Association. Zeolitic chabazite include anaturally occurring tectosilicate mineral of a zeolite group withapproximate formula (Ca,Na₂,K₂,Mg)Al₂Si₄O_(12.6)H₂O (i.e., hydratedcalcium aluminum silicate). Three synthetic forms of zeolitic chabaziteare described in “Zeolite Molecular Sieves,” by D. W. Breck, publishedin 1973 by John Wiley & Sons, which is hereby incorporated by reference.The three synthetic forms reported by Breck are Zeolite K-G, describedin J. Chem. Soc., p. 2822 (1956), Barrer et. Al.; Zeolite D, describedin British Patent No. 868,846 (1961); and Zeolite R, described in U.S.Pat. No. 3,030,181, which are hereby incorporated by reference.Synthesis of another synthetic form of zeolitic chabazite, SSZ-13, isdescribed in U.S. Pat. No. 4,544,538. Synthesis of a synthetic form of anon-zeolitic molecular sieve having the chabazite crystal structure,silicoaluminophosphate 34 (SAPO-34), is described in U.S. Pat. No.4,440,871 and U.S. Pat. No. 7,264,789. A method of making yet anothersynthetic non-zeolitic molecular sieve having chabazite structure,SAPO-44, is described for instance in U.S. Pat. No. 6,162,415.

A synthetic 8-ring small pore molecular sieve (for example having theCHA structure) may be prepared via mixing a source of silica, a sourceof alumina and a structure directing agent under alkaline aqueousconditions. Typical silica sources include various types of fumedsilica, precipitated silica and colloidal silica, as well as siliconalkoxides. Typical alumina sources include boehmites, pseudo-boehmites,aluminum hydroxides, aluminum salts such as aluminum sulfite or sodiumaluminate and aluminum alkoxides. Sodium hydroxide is typically added tothe reaction mixture. A typical structure directing agent for thissynthesis is adamantyltrimethyl ammonium hydroxide, although otheramines and/or quaternary ammonium salts may be substituted or added. Thereaction mixture is heated in a pressure vessel with stirring to yield acrystalline product. Typical reaction temperatures are in the range offrom about 100° C. to about 200° C., for instance from about 135° C. toabout 170° C. Typical reaction times are from about 1 hr to about 30days and in specific embodiments, for instance from 10 hours to 3 days.At the conclusion of the reaction, optionally the pH is adjusted to fromabout 6 to about 10, for example from about 7 to about 7.5 and theproduct is filtered and washed with water. Any acid can be used for pHadjustment, for instance nitric acid. Optionally, the product may becentrifuged. Organic additives may be used to help with the handling andisolation of the solid product. Spray-drying is an optional step in theprocessing of the product. The solid product is thermally treated in airor nitrogen. Alternatively, each gas treatment can be applied in varioussequences or mixtures of gases can be applied. Typical calcinationtemperatures are in from about 400° C. to about 850° C.

Molecular sieves having a CHA structure may be prepared for instanceaccording to methods disclosed in U.S. Pat. Nos. 4,544,538 and6,709,644.

The first and second molecular sieves may each have a silica to aluminaratio (SAR) of from 1 to about 50 or about 5 to about 40.

The present molecular sieves are copper-containing. The copper residesin the ion-exchange sites (pores) of the molecular sieves and may alsobe associated with the molecular sieves but not “in” the pores. Uponcalcination, non-exchanged copper salt decomposes to CuO, also referredto herein as “free copper” or “soluble copper.” The free copper may beadvantageous as disclosed in U.S. Pat. No. 8,404,203. The amount of freecopper may be less than, equal to or greater than the amount ofion-exchanged copper. All copper associated with a molecular sieve ispart of any copper-containing molecular sieve.

The copper-containing molecular sieves are prepared for example viaion-exchange from for example a Na⁺ containing molecular sieve (Na⁺form). The Na⁺ form generally refers to the calcined form without anyion exchange. In this form, the molecular sieve generally contains amixture of Na⁺ and H⁺ cations in the exchange sites. The fraction ofsites occupied by Na⁺ cations varies depending on the specific zeolitebatch and recipe. Optionally, the alkali metal molecular sieves are NH₄⁺-exchanged and the NH₄ ⁺ form is employed for ion-exchange with copper.Optionally, the NH4⁺-exchanged molecular sieve is calcined to theH⁺-form which may also be employed for ion-exchange with copper.

Copper is ion-exchanged into molecular sieves with alkali metal, NH₄ ⁺or H⁺ forms with copper salts such as copper acetate, copper sulfate andthe like, for example as disclosed in U.S. Pat. No. 9,242,238. Forinstance, a Na⁺, NH₄ ⁺ or H⁺ form of a molecular sieve is mixed with anaqueous salt solution and agitated at an elevated temperature for asuitable time. The slurry is filtered and the filter cake is washed anddried.

Further, at least a portion of a catalytically active metal may beincluded during a molecular sieve synthetic process such that a tailoredcolloid contains a structure directing agent, a silica source, analumina source and a metal ion (e.g. copper) source.

The amount of copper in the molecular sieves can be about 0.1 to about10 wt %. Advantageously, the amount of copper in the first molecularsieve can be less than the amount of copper in the second molecularsieve.

In some embodiments, the first molecular sieve can be a low coppermolecular sieve in that it has a lower copper concentration than thesecond molecular sieve. Likewise, the second molecular sieve can be ahigh copper molecular sieve in that it has a higher copper concentrationthan the first molecular sieve. For example, a low copper molecularsieve or a low copper zone, or a low copper layer can have a copperconcentration of about 2.5 wt % or less (e.g., about 0.5 to about 2.5 wt%, about 1 to about 2.5 wt %, or about 2 to about 2.5 wt %). In furtherembodiments, a low copper molecular sieve or a low copper zone, or a lowcopper layer can have a copper concentration of about 0.1 to about 4 wt% or about 0.3 to about 3 wt %. As a further example, a high coppermolecular sieve or a high copper zone, or a high copper layer can have acopper concentration of about 3 wt % or greater (e.g., about 3 to about10 wt %, about 3 to about 8 wt %, about 3 to about 6 wt %, or about 3 toabout 4 wt %).

Amounts of copper in a molecular sieve are reported as the oxide, CuO.

The total dry weight of the molecular sieve includes the anyadded/exchanged metals like copper.

The amount of copper in a molecular sieve, for example analuminosilicate zeolite, may also be defined by the copper to aluminumatomic ratio. For example, the Cu/Al atomic ratio for the presentmolecular sieves may be from about 0.05 to about 0.55. Advantageously,the atomic ratio of Cu to Al in the first molecular sieve is less thanthat of the second molecular sieve.

The molecular sieves of the upstream and downstream zones may be thesame or may be different. For instance, they may be the same ordifferent regarding their SAR. For example, the first molecular sievemay have a SAR lower than, equal to or greater than the SAR of thesecond molecular sieve.

The 8-ring small pore molecular sieves containing copper may each have asodium content (reported as Na₂O on a volatile free basis) of below 2 wt%, based on the total weight of the calcined molecular sieve. In morespecific embodiments, sodium content is below 1 wt % or below 2500 ppm.The molecular sieves may each have an atomic sodium to aluminum ratio ofless than about 0.7, for example from about 0.02 to about 0.7. Themolecular sieves may each have an atomic copper to sodium ratio ofgreater than about 0.5, for example from about 0.5 to about 50.

The present copper-containing molecular sieves may exhibit a BET surfacearea, determined according to DIN 66131, of at least about 400 m²/g, atleast about 550 m²/g or at least about 650 m²/g, for example from about400 to about 750 m²/g or from about 500 to about 750 m²/g. The presentmolecular sieves may have a mean crystal size of from about 10nanometers to about 10 microns, from about 50 nanometers to about 5microns or from about 0.1 microns to about 0.5 microns as determined viaSEM. For instance, the molecular sieve crystallites may have a meancrystal size greater than 0.1 microns or 1 micron and less than 5microns.

The molecular sieves may be provided in the form of a powder or aspray-dried material which is admixed with or coated with suitablemodifiers. Modifiers include silica, alumina, titania, zirconia andrefractory metal oxide binders (for example a zirconium precursor). Thepowder or the sprayed material, optionally after admixing or coating bysuitable modifiers, may be formed into a slurry, for example with water,which is deposited upon a suitable substrate as disclosed for example inU.S. Pat. No. 8,404,203.

The term “catalyst” refers to a material that promotes a chemicalreaction. The catalyst includes the “catalytically active species” andthe “carrier” that carries or supports the active species. For example,molecular sieves including zeolites are carriers/supports for presentcopper active catalytic species. Likewise, refractory metal oxideparticles may be a carrier for platinum group metal catalytic species.

The catalytically active species are also termed “promoters” as theypromote chemical reactions. For instance, the present copper-containingmolecular sieves may be termed copper-promoted molecular sieves. A“promoted molecular sieve” refers to a molecular sieve to whichcatalytically active species are intentionally added.

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) meansselective reduction to N₂.

The term “substrate” refers in general to a monolithic material ontowhich a catalytic coating is disposed, for example a flow-throughmonolith or monolithic wall-flow filter. In one or more embodiments, thesubstrate is a ceramic or metal having a honeycomb structure. Anysuitable substrate may be employed, such as a monolithic substrate ofthe type having fine, parallel gas flow passages extending from an inletend to an outlet end of the substrate such that passages are open tofluid flow. The passages, which are essentially straight paths fromtheir fluid inlet to their fluid outlet, are defined by walls on which acatalytic coating is disposed so that gases flowing through the passagescontact the catalytic material. The flow passages of the monolithicsubstrate are thin-walled channels, which can be of any suitablecross-sectional shape and size such as trapezoidal, rectangular, square,sinusoidal, hexagonal, triangular, etc. Such structures may contain fromabout 60 to about 900 or more gas inlet openings (i.e. cells) per squareinch of cross-section.

Present substrates are 3-dimensional having a length and a diameter anda volume, similar to a cylinder. The shape does not necessarily have toconform to a cylinder. The length is an axial length defined by an inletend and an outlet end.

Flow-through monolith substrates for example have a volume of from about50 in³ to about 1200 in³, a cell density of from about 60 cells persquare inch (cpsi) to about 500 cpsi or up to about 900 cpsi, forexample from about 200 to about 400 cpsi and a wall thickness of fromabout 50 to about 200 microns or about 400 microns.

The substrate may be a “flow-through” monolith as described above.Alternatively, a catalytic coating may be disposed on a wall-flow filtersoot filter, thus producing a Catalyzed Soot Filter (CSF). If awall-flow substrate is utilized, the resulting system will be able toremove particulate matter along with gaseous pollutants. The wall-flowfilter substrate can be made from materials commonly known in the art,such as cordierite, aluminum titanate or silicon carbide. Loading of thecatalytic coating on a wall-flow substrate will depend on substrateproperties such as porosity and wall thickness and typically will belower than the catalyst loading on a flow-through substrate.

Wall-flow filter substrates useful for supporting the SCR catalyticcoatings have a plurality of fine, substantially parallel gas flowpassages extending along the longitudinal axis of the substrate.Typically, each passage is blocked at one end of the substrate body,with alternate passages blocked at opposite end-faces. Such monolithiccarriers may contain up to about 700 or more flow passages (or “cells”)per square inch of cross-section, although far fewer may be used. Forexample, the typical carrier usually has from about 100 to about 300,cells per square inch (“cpsi”). The cells can have cross-sections thatare rectangular, square, triangular, hexagonal, or are of otherpolygonal shapes. Wall-flow substrates typically have a wall thicknessfrom about 50 microns to about 500 microns, for example from about 150microns to about 400 microns. Wall-flow filters will generally have awall porosity of at least 40% with an average pore size of at least 10microns prior to disposition of the catalytic coating. For instance,wall-flow filters will have a wall porosity of from about 50 to about75% and an average pore size of from about 10 to about 30 microns priorto disposition of a catalytic coating.

FIGS. 1 and 2 illustrate an exemplary substrate 2 in the form of aflow-through substrate coated with a washcoat composition as describedherein. Referring to FIG. 1, the exemplary substrate 2 has a cylindricalshape and a cylindrical outer surface 4, an upstream end face 6 and acorresponding downstream end face 8, which is identical to end face 6.Substrate 2 has a plurality of fine, parallel gas flow passages 10formed therein. As seen in FIG. 2, flow passages 10 are formed by walls12 and extend through carrier 2 from upstream end face 6 to downstreamend face 8, the passages 10 being unobstructed so as to permit the flowof a fluid, e.g., a gas stream, longitudinally through carrier 2 via gasflow passages 10 thereof. As more easily seen in FIG. 2, walls 12 are sodimensioned and configured that gas flow passages 10 have asubstantially regular polygonal shape. As shown, the washcoatcomposition can be applied in multiple, distinct layers if desired. Inthe illustrated embodiment, the washcoat consists of both a discretebottom washcoat layer 14 adhered to the walls 12 of the carrier memberand a second discrete top washcoat layer 16 coated over the bottomwashcoat layer 14. The present invention can be practiced with one ormore (e.g., 2, 3, or 4) washcoat layers and is not limited to theillustrated two-layer embodiment.

Alternatively, FIGS. 1 and 3 can illustrate an exemplary substrate 2 inthe form a wall flow filter substrate coated with a washcoat compositionas described herein. As seen in FIG. 3, the exemplary substrate 2 has aplurality of passages 52. The passages are tubularly enclosed by theinternal walls 53 of the filter substrate. The substrate has an inletend 54 and an outlet end 56. Alternate passages are plugged at the inletend with inlet plugs 58, and at the outlet end with outlet plugs 60 toform opposing checkerboard patterns at the inlet 54 and outlet 56. A gasstream 62 enters through the unplugged channel inlet 64, is stopped byoutlet plug 60 and diffuses through channel walls 53 (which are porous)to the outlet side 66. The gas cannot pass back to the inlet side ofwalls because of inlet plugs 58. The porous wall flow filter used inthis invention is catalyzed in that the wall of said element has thereonor contained therein one or more catalytic materials. Catalyticmaterials may be present on the inlet side of the element wall alone,the outlet side alone, both the inlet and outlet sides, or the wallitself may consist all, or in part, of the catalytic material. Thisinvention includes the use of one or more layers of catalytic materialon the inlet and/or outlet walls of the element.

Catalyzed wall-flow filters are disclosed for instance in U.S. Pat. No.7,229,597. This reference teaches a method of applying a catalyticcoating such that the coating permeates the porous walls, that is, isdispersed throughout the walls. Flow-through and wall-flow substratesare also taught for example in U.S. Pat. app. No. 62/072,687, publishedas WO2016/070090.

For example, in the present systems the first substrate is a porouswall-flow filter and the second substrate is a flow-through monolith oralternatively, the first substrate is a flow-through monolith and thesecond substrate is a porous wall-flow filter. Alternatively, bothsubstrates may be identical and may be flow-through or wall-flowsubstrates.

The present catalytic coating may be on the wall surface and/or in thepores of the walls, that is “in” and/or “on” the filter walls. Thus, thephrase “having a catalytic coating thereon” means on any surface, forexample on a wall surface and/or on a pore surface.

The term “exhaust stream” or “exhaust gas stream” refers to anycombination of flowing gas that may contain solid or liquid particulatematter. The stream comprises gaseous components and is for exampleexhaust of a lean burn engine, which may contain certain non-gaseouscomponents such as liquid droplets, solid particulates and the like. Anexhaust stream of a lean burn engine typically further comprisescombustion products, products of incomplete combustion, oxides ofnitrogen, combustible and/or carbonaceous particulate matter (soot) andun-reacted oxygen and/or nitrogen.

Certain embodiments pertain to the use of articles, systems and methodsfor removing NOx from exhaust gases of internal combustion engines, inparticular diesel engines, which operate at combustion conditions withair in excess of that required for stoichiometric combustion, i.e. leanconditions.

The inlet end of a substrate is synonymous with the “upstream” end or“front” end. The outlet end is synonymous with the “downstream” end or“rear” end. A substrate will have a length and a width. An upstream zoneis upstream of a downstream zone. A zone of a catalyzed substrate isdefined as a cross-section having a certain coating structure thereon.

In the present exhaust gas treatment methods, the exhaust gas stream ispassed through the SCR article, SCR system or exhaust gas treatmentsystem by entering the upstream end and exiting the downstream end.

The ceramic substrate may be made of any suitable refractory material,e.g. cordierite, cordierite-a-alumina, aluminum titanate, siliconcarbide, silicon nitride, zircon mullite, spodumene,alumina-silica-magnesia, zircon silicate, sillimanite, a magnesiumsilicate, zircon, petalite, α-alumina, an aluminosilicate and the like.

Substrates useful in the present invention may also be metallic,comprising one or more metals or metal alloys. The metallic substratesmay be employed in various shapes such as pellets, corrugated sheet ormonolithic foam. Specific examples of metallic substrates includeheat-resistant, base-metal alloys, especially those in which iron is asubstantial or major component. Such alloys may contain one or more ofnickel, chromium, and aluminum, and the total of these metals mayadvantageously comprise at least about 15 wt % (weight percent) of thealloy, for instance, about 10 to about 25 wt % chromium, about 1 toabout 8 wt % of aluminum, and from 0 to about 20 wt % of nickel.

A catalytic coating contains one or more carriers containing activecatalytic species. A catalytic coating may typically be applied in theform of a washcoat containing carriers having catalytically activespecies thereon. A washcoat is formed by preparing a slurry containing aspecified solids content (e.g., 10-60% by weight) of carriers in aliquid vehicle, which is then coated onto a substrate and dried andcalcined to provide a coating layer. When multiple coating layers areapplied, the substrate is dried and calcined after each layer is appliedand/or after the number of desired multiple layers are applied.

Coating layers of molecular sieves may be prepared using a binder, forexample, a ZrO₂ binder derived from a suitable precursor such aszirconyl acetate or any other suitable zirconium precursor such aszirconyl nitrate. Zirconyl acetate binder provides a catalytic coatingthat remains homogeneous and intact after thermal aging, for example,when the catalyst is exposed to high temperatures of at least about 600°C., for exam ple, about 800° C. and higher, and high water vaporenvironments of about 10% or more. Other potentially suitable bindersinclude, but are not limited to, alumina and silica. Alumina bindersinclude aluminum oxides, aluminum hydroxides, and aluminumoxyhydroxides. Aluminum salts and colloidal forms of alumina many alsobe used. Silica binders include various forms of SiO₂, includingcolloidal silica. Binder compositions may include any combination ofzirconia, alumina, and silica.

Any of present coating layers may contain ZrO₂ binder and/or Al₂O₃. Thecatalytic coating may comprise more than one thin adherent layer. Thecoating is disposed on and in adherence to the substrate. The entirecoating comprises the individual “coating layers”. The catalytic coatingis “zoned”, comprising zoned catalyst layers. This may also be describedas “laterally zoned”. For example, a first layer may extend from theinlet end towards the outlet end extending about 5% to about 100%, about10% to about 90%, or about 20% to about 50% of the substrate length. Asecond layer may extend from the outlet end towards the inlet endextending about 5% to about 100%, about 10% to about 90%, or about 20%to about 50% of the substrate length. The first and second layers may beadjacent to each other and not overlay each other. Alternatively, thefirst and second layers may overlay a portion of each other, providing athird “middle” zone. The middle zone may for example extend from about5% to about 80% of the substrate length. Alternatively, the first layermay extend from the outlet end and the second layer may extend from theinlet end.

The first and second layers may each extend the entire length of thesubstrate or may each extend a portion of the length of the substrateand may overlay or underlay each other, either partially or entirely.Each of the first and second layers may extend from either the inlet oroutlet end.

The first coating layer may extend the entire length of the substrateand the second coating layer may overlay or underlay a portion or all ofthe first layer. For example, the second coating layer may extend fromthe outlet end towards the inlet end about 10% to about 80% of thesubstrate length.

The second coating layer may extend the entire length of the substrateand the first coating layer may overlay or underlay a portion or all ofthe second layer. For example, the first coating layer may extend fromthe inlet end towards the outlet end about 10% to about 80% of thesubstrate length.

The present zones are defined by the relationship of the first andsecond coating layers. With respect to the first and second coatinglayers, there may only an upstream and a downstream zone or there may bean upstream zone, a middle zone and a downstream zone. Where the firstand second layers are adjacent and do not overlap, there are onlyupstream and downstream zones. Where the first and second layers overlapto a certain degree, there are upstream, downstream and middle zones.Where for example, a first coating layer extends the entire length ofthe substrate and the second coating layer extends from the outlet end acertain length and overlays a portion of the first coating layer, thereare only upstream and downstream zones.

The first and/or second coating layers may be in direct contact with thesubstrate. Alternatively, one or more “undercoats” may be present, sothat at least a portion of the first and/or the second coating layersare not in direct contact with the substrate (but rather with theundercoat). One or more “overcoats” may also be present, so that atleast a portion of the first and/or second coating layers are notdirectly exposed to a gaseous stream or atmosphere (but rather are incontact with the overcoat).

The first and second coating layers may be in direct contact with eachother without a “middle” overlapping zone. Alternatively, the first andsecond coating layers may not be in direct contact, with a “gap” betweenthe two zones. In the case of an “undercoat” or “overcoat” the gapbetween the first and second SCR layer is termed an “interlayer.”

An undercoat is a layer “under” a coating layer, an overcoat is a layer“over” a coating layer and an interlayer is a layer “between” twocoating layers.

The interlayer(s), undercoat(s) and overcoat(s) may contain one or morecatalysts or may be free of catalysts.

The present catalytic coatings may comprise more than one identicallayers, for instance more than one first and/or second layers.

The simplest articles of the present invention comprise a flow-throughsubstrate or a wall-flow filter having a first coating layer extendingfrom the inlet end of the monolith or filter towards the outlet end anda second coating layer extending from the outlet end towards the inletend.

Further disclosed is a SCR article comprising a substrate having a frontupstream end and a rear downstream end defining an axial length, wherethe substrate is coated along the entire length with the second coatinglayer comprising the second copper-containing molecular sieve and wherethe first coating layer comprising the first copper-containing molecularsieve overlays a portion of the second coating layer and extends fromthe inlet end towards the outlet end 10%, 20%, 30%, 40%, 50%, 60%, 70%or 80% or the substrate length. In this instance, the concentration ofcopper in the first coating layer will advantageously be less than thatof the second coating layer.

Also disclosed is a selective catalytic reduction article comprising asubstrate having a front upstream end and a rear downstream end definingan axial length, where the substrate is coated along the entire lengthwith the second coating layer comprising the second copper-containingmolecular sieve and where the first coating layer comprising the firstcopper-containing molecular sieve overlays the entire second coatinglayer. In this instance also, the concentration of copper in the firstcoating layer will advantageously be less than that of the secondcoating layer.

The present catalytic coating, as well as each zone of a catalyticcoating or any section of a coating, is present on the substrate at aloading (concentration) of for instance from about 0.3 g/in³ to about4.5 g/in³ based on the substrate. This refers to dry solids weight pervolume of substrate, for example per volume of a honeycomb monolith. Theamount of base metal, i.e. copper, is only a portion of the catalyticcoating, which also includes the molecular sieve. An amount of copperper volume would for instance be from about 0.2% to about 10% of theabove values. An amount of copper per volume is the copperconcentration. An amount of a copper-containing molecular sieve pervolume is the molecular sieve concentration. Concentration is based on across-section of a substrate or on an entire substrate.

The term “catalytic article” refers to an element that is used topromote a desired reaction. The present catalytic articles comprise asubstrate having a catalytic coating disposed thereon.

A system contains more than one article, for instance, a first SCRarticle and a second SCR article. A system may also comprise one or morearticles containing a reductant injector, a diesel oxidation catalyst(DOC), a soot filter, an ammonia oxidation catalyst (AMOx) or a lean NOxtrap (LNT).

An article containing a reductant injector is a reduction article. Areduction system includes a reductant injector and/or a pump and/or areservoir, etc.

The present treatment system may further comprise a diesel oxidationcatalyst and/or a soot filter and/or an ammonia oxidation catalyst. Asoot filter may be uncatalyzed or may be catalyzed (CSF). For instance,the present treatment system may comprise, from upstream todownstream—an article containing a DOC, a CSF, an urea injector, thepresent zoned SCR article or a first SCR article and a second SCRarticle and an article containing an AMOx. A lean NOx trap (LNT) mayalso be included.

An undercoat layer comprising an AMOx catalyst may be present in thedownstream zone of a substrate. For instance an AMOx undercoat layer mayextend from the outlet end towards the inlet end about 10%, about 20%,about 30%, about 40%, about 50%, about 60%, about 70% or about 80% ofthe substrate length of a present article.

An AMOx undercoat layer may also be present on a second substrate of asecond downstream article. This undercoat layer may extend the entirelength of the second substrate or about 10%, about 20%, about 30%, about40%, about 50%, about 60%, about 70%, about 80% or about 90% of thesecond substrate length.

AMOx catalysts are taught for instance in U.S. Pub. No. 2011/0271664. Anammonia oxidation (AMOx) catalyst may be a supported precious metalcomponent which is effective to remove ammonia from an exhaust gasstream. The precious metal may include ruthenium, rhodium, iridium,palladium, platinum, silver or gold. For example, the precious metalcomponent includes physical mixtures or chemical or atomically-dopedcombinations of precious metals. The precious metal component forinstance includes platinum. Platinum may be present in an amount of fromabout 0.008% to about 2 wt % based on the AMOx catalyst.

The precious metal component is typically deposited on a high surfacearea refractory metal oxide support. Examples of suitable high surfacearea refractory metal oxides include alumina, silica, titania, ceria,and zirconia, as well as physical mixtures, chemical combinations and/oratomically-doped combinations thereof. In specific embodiments, therefractory metal oxide may contain a mixed oxide such as silica-alumina,amorphous or crystalline aluminosilicates, alumina-zirconia,alumina-lanthana, alumina-baria, alumina-ceria and the like. Anexemplary refractory metal oxide comprises high surface area y-aluminahaving a specific surface area of about 50 to about 300 m²/g.

The AMOx catalyst may include a zeolitic or non-zeolitic molecular sievefor example selected from those of the CHA, FAU, BEA, MFI and MOR types.A molecular sieve may be physically mixed with an oxide-supportedplatinum component. In an alternative embodiment, platinum may bedistributed on the external surface or in the channels, cavities orcages of the molecular sieve.

Present embodiments that include a first selective catalytic reductionarticle and a second selective catalytic reduction article may bereferred to as a “multi-component” or “multi-brick” system. A “brick”may refer to a single article such as a monolith or filter.

Advantageously, articles of a multi-component system may each containsubstrates containing zoned coatings as disclosed herein.

The catalytic articles are effective to catalyze the reduction ofnitrogen oxides (NOx) in the presence of a reductant, for exampleammonia or urea. In operation, the reductant is periodically meteredinto the exhaust stream from a position upstream of the SCR article. Theinjector is in fluid communication with and upstream of the SCR article.The injector will also be associated with a reductant reservoir and apump.

Present articles, systems and methods are suitable for treatment ofexhaust gas streams from mobile emissions sources such as trucks andautomobiles. Articles, systems and methods are also suitable fortreatment of exhaust streams from stationary sources such as powerplants.

Ammonia is a typical reductant for SCR reactions for treating exhaust ofstationary power plants while urea is the typical SCR reducing agentused for treatment of exhaust of mobile emissions sources. Ureadecomposes to ammonia and carbon dioxide prior to contact with or on theSCR catalyst, where ammonia serves as the reducing agent for NOx.

The articles, systems and methods described herein can provide highNO_(x) conversion. For example, a present catalytic article may exhibitan aged NO_(x) conversion at 200° C. of at least 50%, at least 55% or atleast 60% measured at a gas hourly space velocity of 80000 h⁻¹. Apresent catalytic article may exhibit an aged NO_(x) conversion at 450°C. of at least 70%, at least 75% or at least 80% measured at a gashourly volume-based space velocity of 80000 h⁻¹ under steady stateconditions in a gas mixture of 500 ppm NO, 500 ppm NH₃, 10% O₂, 5% H₂O,balance N₂. The cores are hydrothermally aged in a tube furnace in a gasflow containing 10% H₂O, 10% O₂, balance N₂ for 5 hours at 750° C. SuchSCR activity measureme nts are demonstrated in U.S. Pat. No. 8,404,203.

Further, articles, systems and methods herein may provide NOx conversionunder transient HDD FTP conditions of ≥90% and also an N₂O formation of≤1.5%.

For example, some present selective catalytic reduction articles orsystems are capable of providing NOx conversion of ≥90% and N₂Oformation of ≤40% compared to the NOx conversion and N₂O formation of anarticle or system, respectively, containing a uniform concentration ofCuCHA as the only SCR catalyst under transient engine testingconditions. An article containing a uniform concentration of CuCHAcontains a catalytic coating comprising a CuCHA at a uniformconcentration on the substrate; CuCHA is the only SCR catalyst presentas a reference. Likewise, as a system reference, both substrates containuniform concentrations of the same CuCHA as the only SCR catalyst.

That is, present articles and systems provide as good or better NOxconversion while forming less N₂O.

SCR performances such as the NO, conversion and N₂O formation are forexample measured at a gas hourly volume-based space velocity of 80000h⁻¹ under pseudo-steady state conditions in a gas mixture of 500 ppm NO,(fast SCR condition: NO₂/NOx=0.5 or standard SCR conditions: NO₂/NOx=0),500 ppm NH₃, 10% O₂, 5% H₂O, balance N₂ in a temperature ramp of 0.5°C./min from 200° C. to 600° C.

NOx conversion is defined as mol% conversion of NO and NO₂ combined. Ahigh value is desired. N₂O formation is defined as mol% conversion of NOand NO₂ combined to N₂O. A low value is desired. Percent conversion ofNOx to N₂O is calculated based on the assumption that each molecule ofN₂O is derived from one molecule of NOx and one molecule of NH₃.

Present selective catalytic reduction articles or systems or methods arefor example capable of providing >90% total NOx conversion where thefront upstream zone provides from about 30% to about 80% of the totalNOx conversion, for example measured under transient HDD FTP conditions.

Exemplary embodiments of the invention are shown below. It is understoodthat the embodiments are provided as examples, and further combinationsof catalytic coatings are encompassed. Further, as exemplified, coatingzones and coating layers may be interchangeable in that a coating layermay define a coating zone.

In one embodiment, as seen in FIG. 4a , a substrate 100 can be coatedwith a single coating layer 101 that is a combination of multiplecatalytically active molecular sieves. For example, the single coating101 can be a combination of a copper-containing molecular sieve in a lowcopper concentration (e.g., about 0.1 to about 3 wt % copper), and acopper-containing molecular sieve in a high copper concentration (e.g.,about 3 to about 10 wt %).

In a further embodiment, a substrate 100 can be coated with twonon-overlapping zones. As seen in FIG. 4b , a first zone 102 proximateto the front or inlet end 100 a of the substrate 100 can comprisecopper-containing molecular sieve in a low copper concentration (e.g.,about 0.1 to about 3 wt % copper). A second zone 103 proximate to therear or outlet end 100 b of the substrate 100 can comprisecopper-containing molecular sieve, preferably at a high copperconcentration (e.g., about 3 to about 10 wt %).

In a further embodiment, As seen in FIG. 4c , a substrate 100 can becoated with a first coating layer 104 extending from the front or inletend 100 a of the substrate 100 to the rear or outlet end 100 b of thesubstrate 100 and a second coating layer 105 that is coated over thefirst coating layer 104 proximate to the rear or outlet end 100 b of thesubstrate 100 and extending across only a partial length of thesubstrate 100 (i.e., terminating before reaching the front or inlet end100 a of the substrate100). The first layer 104 can comprisecopper-containing molecular sieve in a low copper concentration (e.g.,about 0.1 to about 3 wt % copper). The second layer 105 can comprisecopper-containing molecular sieve, preferably at a high copperconcentration (e.g., about 3 to about 10 wt %).

In still a further embodiment, as seen in FIG. 4d , a substrate 100 canbe coated with a first coating layer 106 extending from the front orinlet end 100 a of the substrate 100 to the rear or outlet end 100 b ofthe substrate 100 and a second coating layer 107 that is coated over thefirst coating layer 106 proximate to the front or inlet end 100 a of thesubstrate 100 and extending across only a partial length of thesubstrate 100 (i.e., terminating before reaching the rear or outlet end100 b of the substrate 100). The first coating layer 106 can comprisecopper-containing molecular sieve, preferably at a high copperconcentration (e.g., about 3 to about 10 wt %). The second coating layer107 can comprise copper-containing molecular sieve in a low copperconcentration (e.g., about 0.1 to about 3 wt % copper).

In another embodiment, as seen in FIG. 4e , a substrate 100 can becoated with a first coating layer 108 extending from the front or inletend 100 a of the substrate 100 to the rear or outlet end 100 b of thesubstrate 100 and a second coating layer 109 that is coated over thefirst coating layer 108 also extending from the front or inlet end 100 aof the substrate 100 to the rear or outlet end 100 b of the substrate100. The first coating layer 108 can comprise copper-containingmolecular sieve, preferably at a high copper concentration (e.g., about3 to about 10 wt %). The second coating layer 109 can comprisecopper-containing molecular sieve in a low copper concentration (e.g.,about 0.1 to about 3 wt % copper).

In yet another embodiment, as seen in FIG. 4f , a first substrate 100can be coated with a first coating layer 110, and a second, separatesubstrate 100′ can be coated with a second coating layer 111. The firstcoating layer 110 on the first substrate 100 can comprisecopper-containing molecular sieve in a low copper concentration (e.g.,about 0.1 to about 3 wt % copper). The second coating layer 111 on thesecond, separate substrate 100′ can comprise copper-containing molecularsieve, preferably at a high copper concentration (e.g., about 3 to about10 wt %). The first substrate 100 is upstream from the second, separatesubstrate 100′ relative to the flow path of an exhaust stream. The firstcoating layer 110 can extend from a front or inlet end 100 a to a rearor outlet end 100 b of the first substrate 100, and the second coatinglayer 111 can extend from a front or inlet end 100a′ to a rear or outletend 100 b′ of the second substrate 100′.

In a further embodiment, as seen in FIG. 4g and FIG. 4 i, a substrate100 can be coated with a first coating layer 112 proximate to the frontor inlet end 100 a of the substrate 100 and extending only partiallyalong the length of the substrate 100 (i.e., terminating before reachingthe rear or outlet end 100 b of the substrate 100). The substrate 100can be coated with a second coating layer 113. As seen in FIG. 4g , thesecond coating layer 113 extends from the front or inlet end 100 a ofthe substrate 100 to the rear or outlet end 100 b of the substrate 100(and thus is coated completely over the first coating layer 112). Asseen in FIG. 4i , the second coating layer 113 extends from the rear oroutlet end 100 b of the substrate 100 only a partial length toward thefront or inlet end 100 a of the substrate 100 to a point so that thesecond coating layer 113 is coated over a portion of the substrate 100and also over a portion of the first coating layer 112. The firstcoating layer 112 on the substrate 100 can comprise copper-containingmolecular sieve in a low copper concentration (e.g., about 0.1 to about3 wt % copper). The second coating layer 113 on the substrate 100 cancomprise copper-containing molecular sieve, preferably at a high copperconcentration (e.g., about 3 to about 10 wt %). As described above, thesecond coating layer 113 can partially cover the first coating layer 112or completely cover the first coating layer 112.

In an additional embodiment, as seen in FIG. 4h and FIG. 4j , asubstrate 100 can be coated with a first coating layer 115 proximate tothe rear or outlet end 100 b of the substrate 100 and extending onlypartially along the length of the substrate 100 (i.e., terminatingbefore reaching the front or inlet end 100 a of the substrate 100). Thesubstrate 100 can be coated with a second coating layer 114. As seen inFIG. 4h , the second coating layer 114 extends from the front or inletend 100 a of the substrate 100 to the rear or outlet end 100 b of thesubstrate 100 (and thus is coated completely over the first coatinglayer 115). As seen in FIG. 4j , the second coating layer 114 extendsfrom the front or inlet end 100 a of the substrate 100 only a partiallength toward the rear or outlet end 100 b of the substrate 100 to apoint so that the second coating layer 114 is coated over a portion ofthe substrate 100 and also over a portion of the first coating layer115. The first coating layer 115 on the substrate 100 can comprisecopper-containing molecular sieve in a low copper concentration (e.g.,about 0.1 to about 3 wt % copper). The second coating layer 114 on thesubstrate 100 can comprise copper-containing molecular sieve, preferablyat a high copper concentration (e.g., about 3 to about 10 wt %). Asdescribed above, second coating layer 114 can partially cover the firstcoating layer 115 or completely cover the first coating layer 115.

“Platinum group metal components” refer to platinum group metals or oneof their oxides. “Rare earth metal components” refer to one or moreoxides of the lanthanum series defined in the Periodic Table ofElements, including lanthanum, cerium, praseodymium and neodymium.

“Substantially free” means for instance “little or no”, for instance,means “no intentionally added” and having only trace and/or inadvertentamounts. For instance, it means less than 2 wt % (weight %), less than1.5 wt %, less than 1.0 wt %, less than 0.5 wt %, 0.25 wt % or less than0.01 wt %, based on the weight of the indicated total composition.

“Substantially all” means for example at least 90% at least 91%, atleast 92%, at least 93%, at least 94%, at least 95%, at least 96%, atleast 97%, at least 98%, at least 99% or at least 99.5%, by weight or bynumber.

The articles “a” and “an” herein refer to one or to more than one (e.g.at least one) of the grammatical object. Any ranges cited herein areinclusive. The term “about” used throughout is used to describe andaccount for small fluctuations. For instance, “about” may mean thenumeric value may be modified by ±5%, ±4%, ±3%, ±2%, ±1%, ±0.5%, ±0.4%,±0.3%, ±0.2%, ±0.1% or ±0.05%. All numeric values are modified by theterm “about” whether or not explicitly indicated. Numeric valuesmodified by the term “about” include the specific identified value. Forexample “about 5.0” includes 5.0.

Unless otherwise indicated, all parts and percentages are by weight.Weight percent (wt %), if not otherwise indicated, is based on an entirecomposition free of any volatiles, that is, based on dry solids content.

All U.S. patent applications, published patent applications and patentsreferred to herein are hereby incorporated by reference.

EXAMPLE 1 SCR Articles, Preparation and Testing

Catalytic coatings containing CuCHA zeolite are disposed via a washcoatprocess on cellular ceramic monoliths having a cell density of 400 cpsiand a wall thickness of 6 mil. The coated monoliths are dried at 110° C.and calcined at about 450° C. for 1 hour. The coating process provides acatalyst loading of 3 g/in³. The front and rear zones are of equalcoating volume. All samples are hydrothermally aged in the presence of10% H₂O/air at 750° C. for 5 hours. The front zone extends from theinlet end of the core to about 50% of the length and the rear zoneextends from the outlet end of the core to about 50% of the length ofthe core. Reference samples have uniform coatings.

SCR testing of aged samples is performed in HDD FTP (Heavy Duty DieselUS Federal Test Procedure) cycle conditions. The transient temperatureof the HDD FTP test ranges from 225° C. and 325° C. The cumulative inletNOx per cycl e (1200 sec) is 5 g/L. The transient space velocity rangesfrom 20K to 120K hr⁻¹. Reported are HDD FTP NOx conversion and N₂Oformation results. Front and rear zone copper is weight %, based on thetotal weight of the zeolite. Weight percent Cu is reported as CuO.

NOx conversion is defined as mol% conversion of NO and NO₂ combined. Ahigh value is desired. N₂O formation is defined as mol% conversion of NOand NO₂ combined to N₂O. A low value is desired. Percent conversion ofNOx to N₂O is calculated based on the assumption that each molecule ofN₂O is derived from one molecule of NOx and one molecule of NH₃.

Reference Comparative Examples with Equal Front and Rear Cu Loadings

front zone Cu rear zone Cu NOx conversion N₂O formation (wt %) (wt %)(%) (%) ref1) 0.6 0.6 86.6 1.0 ref2) 1.2 1.2 91.1 1.7 ref3) 2.3 2.3 93.82.5 ref4) 2.7 2.7 94.4 2.8 ref5) 3.4 3.4 93.8 3.0Inventive Zoned CuCHA/CuCHA with Different Front and Rear Cu Loadings

front zone Cu rear zone Cu NOx conversion N₂O formation (wt %) (wt %)(%) (%) 1a) 0.6 1.2 91.6 1.0 1b) 0.6 2.3 93.6 1.1 1c) 0.6 2.7 94.4 1.51d) 0.6 3.4 94.4 1.3 1e) 1.2 2.3 94.6 1.8 1f) 1.2 2.7 92.0 1.8 1g) 1.23.4 93.6 1.8 1h) 2.3 2.7 95.7 2.3 1i) 2.3 3.4 92.9 2.5 1j) 2.7 3.4 92.72.8

It is seen that inventive samples 1a-1j exhibit excellent NOx conversion(>91%) while reducing N₂O formation compared to the reference samplesresulting in overall better performance. To achieve NOx conversion of93-95%, uniform copper loadings result in N₂O formation of from 2.5 to3.0, while the present zoned copper substrates result in N₂O formationof from 1.1% to 1.8%. Inventive samples 1b-1g achieve an NOx conversionof at least 92% and a maximum N₂O formation of 1.8%.

1. A selective catalytic reduction article comprising a substrate havinga front upstream end and a rear downstream end defining an axial lengthof the substrate and having a catalytic coating thereon, wherein thecatalytic coating comprises: a first coating layer comprising a firstcopper-containing molecular sieve; and a second, different coating layercomprising a second copper-containing molecular sieve.
 2. The selectivecatalytic reduction article of claim 1, wherein the catalytic coating iszoned and comprises: a first zone proximate to the front upstream end ofthe substrate, the first zone including the first coating layercomprising the first copper-containing molecular sieve; and a secondzone proximate to the rear downstream end of the substrate, the secondzone including the second coating layer comprising the second, differentcopper-containing molecular sieve.
 3. The selective catalytic reductionarticle of claim 2, wherein the first copper-containing molecular sievein the first zone has a copper concentration that is less than or equala copper concentration of the second, different copper-containingmolecular sieve in the second zone.
 4. The selective catalytic reductionarticle of claim 1, wherein the substrate is a porous wall-flow filteror a flow-through monolith.
 5. The selective catalytic reduction articleof claim 1, wherein the first copper-containing molecular sievecomprises copper oxide in an amount of about 0.1 to about 4 wt %, andthe second copper-containing molecular sieve comprises copper oxide inan amount of about 3 to about 10 wt %, based on the total weight of themolecular sieve.
 6. The selective catalytic reduction article of claim1, wherein the first copper-containing molecular sieve comprises copperoxide in an amount of about 1 to about 2.5 wt %, and the secondcopper-containing molecular sieve comprises copper oxide in an amount ofabout 3 to about 6 wt %, based on the total weight of the molecularsieve.
 7. The selective catalytic reduction article of claim 1, whereina Cu/Al atomic ratio for each of the first copper-containing molecularsieve and the second copper-containing molecular sieve is independentlyabout 0.05 to about 0.55, and wherein the Cu/Al atomic ratio of thefirst copper-containing molecular sieve is less than the Cu/Al atomicratio of the second copper-containing molecular sieve.
 8. The selectivecatalytic reduction article of claim 1, wherein the first coating layerextends a distance from the front, upstream end of the substrate towardsthe rear, downstream end of the substrate and overlays a portion of thesecond coating layer, which extends from the rear, downstream end of thesubstrate a distance towards the front, upstream end of the substrate.9. The selective catalytic reduction article of claim 1, wherein thefirst coating layer extends a distance from the front, upstream end ofthe substrate to the rear, downstream end of the substrate and overlaysan entirety of the second coating layer, which extends from the rear,downstream end of the substrate to the front, upstream end of thesubstrate.
 10. The selective catalytic reduction article of claim 1,wherein the second coating layer extends a distance from the front,upstream end of the substrate towards the rear, downstream end of thesubstrate and overlays a portion of the first coating layer, whichextends a distance from the rear, downstream end of the substratetowards the front, upstream end of the substrate.
 11. The selectivecatalytic reduction article of claim 1, wherein the second coating layerextends from the front, upstream end of the substrate to the rear,downstream end of the substrate and overlays an entirety of the firstcoating layer, which extends from the rear, downstream end of thesubstrate to the front, upstream end of the substrate.
 12. The selectivecatalytic reduction article of claim 1, wherein the first coating layerand the second coating layer are adjacent and do not overlay each other.13. The selective catalytic reduction article of claim 1, wherein thefirst coating layer and the second coating layer are in direct contactwith each other.
 14. The selective catalytic reduction article of claim1, wherein the first copper-containing molecular sieve and the secondcopper-containing molecular sieves are each 8-ring small pore molecularsieves.
 15. The selective catalytic reduction article of claim 14,wherein the first copper-containing molecular sieve and the secondcopper-containing molecular sieve are both independently zeolites havinga structure selected from the group consisting of AEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT and SAV.
 16. The selective catalyticreduction article of claim 14, wherein each of the firstcopper-containing molecular sieve and the second copper-containingmolecular sieve are aluminosilicate zeolites having a CHA crystalstructure and a silica to alumina ratio (SAR) of about 5 to about 40.17. The selective catalytic reduction article of claim 1, wherein thesubstrate includes an undercoat comprising an ammonia oxidation catalyst(AMOx) in the second zone.
 18. A selective catalytic reduction systemcomprising: a first selective catalytic reduction article comprising afirst substrate including a first catalytic coating layer comprising afirst copper-containing molecular sieve having a first amount of copperoxide; and a second selective catalytic reduction article comprising asecond substrate including a second catalytic coating layer comprising asecond copper-containing molecular sieve having a second amount ofcopper oxide that is greater than the first amount of copper oxide;wherein the first selective catalytic reduction article and the secondselective catalytic reduction article are in fluid communication. 19.The selective catalytic reduction system of claim 18 wherein the firstsubstrate of the first selective catalytic reduction article is zoned soas to include a first catalytic coating layer with a first copperconcentration and a second cocatalyst layer with a second copperconcentration that is higher than the first copper concentration. 20.The selective catalytic reduction system of claim 18, wherein the firstsubstrate and the second substrate are each independently selected fromthe group consisting of a porous wall-flow filter and a flow-throughmonolith.
 21. The selective catalytic reduction system of claim 18,wherein the second substrate includes an undercoat comprising an ammoniaoxidation catalyst (AMOx).
 22. An exhaust gas treatment systemcomprising: a selective catalytic reduction article according to claim1; and a reductant injector in fluid communication with and upstream ofthe selective catalytic reduction article; and optionally one or more ofa diesel oxidation catalyst, a soot filter, an ammonia oxidationcatalyst, and an internal combustion engine. 23-24. (canceled)
 25. Amethod for treating an exhaust stream containing NOx, comprising passingthe exhaust stream through a selective catalytic reduction articleaccording to claim
 1. 26. An exhaust gas treatment system comprising: aselective catalytic reduction system according to claim 18; a reductantinjector in fluid communication with and upstream of the selectivecatalytic reduction system; and optionally one or more of a dieseloxidation catalyst, a soot filter, an ammonia oxidation catalyst, and aninternal combustion engine.
 27. A method for treating an exhaust streamcontaining NOx, comprising passing the exhaust stream through aselective catalytic reduction system according to claim
 18. 28. A methodfor treating an exhaust stream containing NOx, comprising passing theexhaust stream through an exhaust gas treatment system according toclaim
 22. 29. A method for treating an exhaust stream containing NOx,comprising passing the exhaust stream through an exhaust gas treatmentsystem according to claim 26.